Influence of the type of energy supply on LH secretion, follicular growth and response to estrus synchronization treatment in feed-restricted suckler beef cows
2000
Ponsart, C. | Khireddine, B. | Ponter, A.A. | Humboldt, P. | Mialot, J.P. | Grimard, B.
The present experiment aimed to compare the efficiency of supplementation (+17.5 MJ Net Energy/d starting 47+/-4 days after calving) with concentrate (CS, maize grain, n=10) or with forage (FS, maize silage, n=10) in estrus-synchronized (Norgestomet implant 10 days inserted 60+/-4 days postpartum + PMSG at implant removal) beef cows previously restricted (47 MJ Net Energy/d, 785 g CP/d, 70% of requirements). The type of diet had no significant effect on basal LH concentrations (CS: 0.18+/-0.12 vs FS: 0.11+/-0.02 ng/mL), LH pulse frequency (CS: 0.7+/-0.3 vs FS: 0.8+/-0.2 pulse/10 h), LH pulse amplitude (CS: 0.55+/-0.50 vs FS: 0.62+/-0.50 ng/mL) or estradiol (E2) concentrations (CS: 3.3+/-0.8 vs FS: 4.6+/-0.8 pg/mL) 13 days after the beginning of energy supplementation. No differences between CS and FS cows were observed for the number of small, medium and large follicles nor on the size of the largest follicle from 11 days before implant insertion to implant removal (IR). After IR, an LH surge was observed in 2 of the CS and 4 of the FS cows. The type of energy supplementation had no significant effect on LH (CS: 0.16+/-0.06 ng/mL vs FS 0.48+/-0.06 ng/mL; P>0.05) or on estradiol concentrations (CS: 7.8+/-0.2 vs FS: 8.9+/-0.2 pg/mL, P>0.10) measured hourly from 29 to 49 h after IR. Cows that ovulated after IR tended to have higher E2 concentrations than cows that did not ovulate (9.4+/-0.2 vs 6.3+/-0.2 pg/mL, P=0.08). Similar ovulation and pregnancy rates were observed in CS and FS cows (CS: 6/10 vs FS: 7/10 and CS: 6/10 vs FS: 5/10 respectively, P>0.05). To conclude, energy supplementation with forage was as effective as energy supplementation with concentrate to influence follicular growth, ovulation and pregnancy percentage after estrus synchronization treatment in diet-restricted beef cows.
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